Infection in the golden hamster with Leishmania donovani is being used as a model for the study of immunity to visceral leighmaniasis. Subcutaneously injected hamsters have been found to develop some resistance to infection while intracardially injected hamsters rapidly succumb to progressive disease. Consequently, these two inoculation routes are being utilized to produce experimental infections for comparative immunological studies. Antigen specific responses, as assayed by delayed hypersensitivity and blast transformation, as well as generalized lymphoid cell function are being assessed in these resistant and "anergic" animals. Attempts are being made to determine if parasite visceralization occurs because of a failure to generate an effective immune response or whether the presence of parasites within lymphoid tissues leads to a state of desensitization by interfering with normal cell to cell interactions. Additional studies are being performed to determine if macrophages from hamsters and/or man can be activated to a degree necessary for these cells to exhibit intracellular killing of L. donovani amastigotes.